Transcript Development of a Time Projection Chamber Using Gas Electron

Development of a Time
Projection Chamber Using Gas
Electron Multipliers (GEM-TPC)
Susumu Oda, H. Hamagaki, K. Ozawa, M. Inuzuka,
T. Sakaguchi, T. Isobe, T. Gunji, S. Saito, Y. Morino,
Y.L. Yamaguchi1, S. Sawada2 and S. Yokkaichi3
CNS, University of Tokyo, 1Waseda University, 2KEK, 3RIKEN
1. Motivation of GEM-TPC Development
2. GEM-TPC prototype
3. Performance Evaluation of GEM-TPC
4. Summary
2005/10/25 Puerto Rico IEEE NSS 2005 N17-8
1/13
2/13
Motivation of GEM-TPC
development

Study hot and dense matter, Quark Gluon
Plasma (QGP), by high energy heavy ion collision.
– e.g. PHENIX-RHIC-BNL, ALICE-LHC-CERN

A high resolution (position, double track and energy)
tracker under high collision rate and high particle density
is needed.
– Interested pT region is 0.2 - 20GeV/c  magnetic field should be kept low
~1T.
– Required resolution dpT/pT2~10-3 (GeV/c)-1 : to resolve Upsilon states etc.
– If 1-m radius solenoidal tracker, 200mm of spatial resolution is required.
– Since particle density is high, double tracks with >1cm should be
separated.

TPC using GEM（Gas Electron Multiplier）may satisfy the above
requirements.
– Ion feedback suppression.
– No incidental angle dependence by 2-dimension symmetry.
– Flexibility for magnification.
3/13
GEM-TPC prototype


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Field cage : 35cm(drift direction) x 17cm x 17cm
Triple-GEM : 10cm x 10cm (effective region), made in
CERN.
Pad : rectangular & zigzag 1.09mm x 12mm
Charge sensitive preamplifier : time constant 1ms
24ch signals are read out using 100MHz FADC.
Beam direction
Beam direction
4/13
Gas

3 kinds of gases with
different drift velocity and
diffusion coefficient were
used for measurement.
 Energy resolution was s=1013% with 55Fe X-ray source.
Electric
field
Drift
velocity
Transverse
diffusion
@1cm
Longitudinal
diffusion
@1cm
Ar(90%)-CH4(10%)
130 V/cm
5.48 cm/ms
570 mm
378 mm
Ar(70%)-C2H6(30%)
390 V/cm
5.01 cm/ms
306 mm
195 mm
CF4
570 V/cm
8.90 cm/ms
104 mm
82 mm
55Fe
X-ray
(5.9keV)
spectrum
with CF4
s=13%
5/13
Beam test

A beam test was performed at KEK PS to evaluate the
performance of the GEM-TPC.
 Three kinds of gases
– Ar-CH4(P10), Ar-C2H6 and CF4

Evaluated items
–
–
–
–
–
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Detection efficiency (1GeV/c p)
Spatial resolution (1GeV/c p)
Effect of beam rate (2GeV/c e,p,p)
PID by dE/dx measurement (0.5-3GeV/c、e,m,p,p,d)
Double track resolution (2GeV/c e,p,p)
Without magnetic field.
Setup schematic view
6/13
Typical GEM-TPC signal
ADC
Track
Ar-C2H6, drift length 85mm,
rectangular pad
1GeV/c electron beam
Time (6.4ms=640bin, 1bin=10ns)
7/13
Result 1: Detection efficiency
2. For events with hits in 1st pad row
and 3rd pad row, the fraction of hit
in 2nd pad row.
The plateau reaches 99.5%.
To be updated
– Detection efficiencies of Ar+C2H6
and CF4 are also >99.5%
99.5%
8/13
Result 2: Spatial resolution
1.
2.
Hit positions in pad-row direction (X) and drift direction (Z) are determined by
weighted mean of charge.
Spatial resolution is estimated from residuals between position of inner row
and interpolated position.
1
2
Res X  X 1 
2
 X 0  X 2 , s X

6
s Res
x
Result

Best resolution was 80mm (X-direction) and 310mm(Z-direction) with Ar-C2H6
gas, with rectangular pad, for drift length of 13mm.

Zigzag pad and rectangular pad have similar spatial resolution.
9/13
Result 3: Beam rate dependence
Purpose
To study the effect of ion feedback on the GEM-TPC
performance, detection efficiency and spatial
resolution were evaluated as indexes.

Beam rate was changed by changing the width of
beam slit.
 Beam rate was monitored by 2.5x2.5cm2 plastic
scintillator.
 Ar-CH4 gas and 85mm drift
Result
 Under large beam rate (<5000cps/cm2, ~105cps),
high detection efficiency was obtained.
 Spatial resolution worsen by a factor of 10%.
 RHIC (Au-Au, sNN=200GeV)
<dNch/dh>|h=0=170, Luminosity=1.4x1027/cm2/s,
sinel=7barn
⇒300cps/cm2 : 30cm away from vertex

LHC (Pb-Pb, sNN=5.5 TeV)
<dNch/dh>|h=0~1000, Luminosity~1x1027/cm2/s,
sinel~8barn
⇒1400cps/cm2 : 30cm away from vertex
10/13
Result 4: Particle
identification
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Energy loss was measured in momentum
range of 0.5 - 3.0GeV/c with Ar-CH4.
Since gain fluctuated between each
momentum, energy loss was corrected as
the measured values of pion agree with
calculated values of pion (max. 30%)
Energy resolution of a larger TPC was
evaluated from measured distribution
(1.0GeV/c beam)
–
–
With a 50cm track, energy resolution is
expected to be 9.1% for pion and 8.0% for
proton
Better than STAR TPC
• sE/E=8% with a 67cm track
Expected energy loss
spectra of 1.0GeV/c p+ and
p beams with 50cm track
For proton efficiency of 99%,
p rejection factor is 180
p
p
Energy loss
1.0GeV/c p+
11/13
Result 5: Double
track resolution
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Double track resolution was evaluated by
the distribution of distance between two hits
in drift direction
Multiple hits in one event (6.4ms) were
generated by high beam rate
(~4000cps/cm2) and a lead block (1X0)
Since distance between scattered
secondary particles is generally less than
20mm, those distribution was evaluated
from data with low beam rate
For Ar+CH4 gas and 85mm of drift length,
diffusion is 1.7mm(transeverse) and
1.0mm(longitudinal)
Two tracks with 12mm distance can be
distinguished
Longitudinal diffusion is 1mm and electric
noise limits double track resolution
Secondary
particle
Accidental
coincidence
12/13
Summary and Outlook

A GEM-TPC prototype was constructed toward a tracker
works under high rate and high multiplicity circumstance
Beam test for evaluation of GEM-TPC was done
To be updated

– Detection efficiency : 99.5%
– Spatial resolution : 80mm (X direction), 310mm (Z direction)
(Ar(70%)+C2H6(30%))
– Beam Rate : Spatial resolution was unchanged even with
5000cps/cm2
– Energy loss : Fluctuation of gain was 12% in maximum
– Adjacent track resolution : 12mm (Z direction)

Our expectation was mostly satisfied

GEM
13/13
Development of GEM in Japan
We succeeded in fabricating a new type of GEM
(CNS-GEM) using a dry etching method.
CERN-GEM
Etching
method
wet etching
CNS-GEM
dry etching
The cross
section of
a hole
A hole with
double-conical
shape

A hole with
cylindrical
shape
Gain stability of CNS-GEM is better than that of
CERN-GEM.
– The shape of holes in GEM significantly affect gain
stability.